This research seeks to advance out understanding of the neurophysiology of the retina. Experiments will be performed to study fundamental issues in Contrast Vision, Color Coding and Dark Adaptation. This will be done by analyzing the light-evoked responses of bipolar cells, amacrine cells, horizontal cells, cones, and ganglion cells. The research will be performed on animals which offer unique opportunities for intracellular recording. Many of the experiments parallel psychophysical work so the results could lead to new models for clinical disorders in contrast perception and dark adaptation. Signals for luminance contrast will be studied in the mudpuppy (Necturus maculosus). Data will be obtained to analyze the significance of the dual organization of bipolar cells, the properties and bases of "contrast rectification" in amacrine cells, the interrelationship of signals generated by negative and positive contrast, and the effect of the glutamate agonist, L 2-amino-4 phosphono-butyrate (APB, L-AP4), on contrast signals. The second project seeks to clarify the role of chromatic-type horizontal cells (C cells) in retinal function. The main approach will consist of injecting current in C cells and recording the effect in ganglion cells. Other key elements include the use of a freshwater fish (the bowfin, Amia calva) which has special advantages for such work, new techniques for isolating the impulse discharge of ganglion cells, and new experimental paradigms (the L spectrum and red/green exchange). The third project will study dark adaptation in cone photoreceptor cells. Special features include the use of a superfused slice preparation of the turtle eyecup and a helium-neon laser to generate intense adapting lights. Dark adaptation curves covering nearly 8 log units will be obtained, some 5 log units greater than yet studied in vertebrate cones. Other experiments will analyze membrane potential, temporal resolution, voltage-sensitive mechanisms and pigment regeneration during dark adaptation.